I like this quote from the movie:
Other animals live in the present. Humans can not. So they invented hope. It's something I can think about.
I like the movie in general for breaking with storytelling conventions in an artful way without being so hard to follow that I just want to switch it off sighingly while exclaiming: "I guess it's art."
I may not understand the metaphors, which no doubt are plentiful throughout the movie, and therefor may not even understand what it is about or what Charlie Kaufman wants to say. But it certainly holding plenty of opportunities ready for letting the viewer get carried away by the movie's discussions about essential questions that are probably part of anybody's life at some point. I certainly got carried away to musing about all sorts of things several times. The discussions between the both main characters are often poetic and their course often takes on unexpected little turns. There are many things in that movie that I've not seen done well prior to this.
CW, in case you want to watch it: Suicide, Depression, Death and touching other unpleasant topics here and there
There's one other thing that I like about this movie: Parts of it are the most dream-like scenes that I've seen in any movie, as far as I can remember. I've been yearning for more accurate representations of the phenomenological idiosyncrasies of dreams for a while. Depending on the genre, filmmakers have tried different approaches, used many different effects and took advantage of technological innovations, as the were made, to depict dream scenes. Turns out all you need is a flatbed editor (or scissors and some tape or whatever editors used initially).
"I'm Thinking Of Ending Things" was the Charlie Kaufmann film that made me look up who wrote it. I've seen two movies of him before. But now I also know his name, somewhat his style, and much more of his work.